In semiconductor device development and nano-material development, electric charged particle beam microscopes and electric charged particle beam microscopy capable of analyzing specimen structure at a spatial resolution power of an order of nanometer (nm) are essential. The electric charged particle beam microscopes are categorized into various types according to the beams to be used. One of these microscopes is a scanning transmission electron microscope (STEM) that scans over a specimen with a converged narrow electron beam and detects electron beams that have been transmitted through the specimen to form an image, and another is a scanning electron microscope (SEM) that detects secondary electrons and backscattered electrons to form an image. Ion microscopes using ions as incident beams are also a type of electric charged particle beam microscopes. One of the major features of these microscopes is their high resolution power, which is a point to consider for microscope development. Specimen drift is an inhibiting factor in achieving high resolution. Specimen drift may cause blurring and distortion in formed images. Whether an image becomes blurred or distorted depends on the imaging modes. A fast-scan mode rapidly scans beams to capture a plurality of image frames and then integrates the image frames to form an image to be stored, while a slow-scan mode forms an image to be stored by a single slow scanning operation. In the fast-scan mode, specimen drift causes image shifts between the frames. The integrated image shifts result in a stored image having blurring in the drift direction. If there is an original image as shown in FIG. 2A and specimen drift occurs, the image undergoes blurring in areas indicated by a hatch pattern in FIG. 2B. On the other hand, the specimen drift occurring during the slow-scan mode operation causes image distortion in the drift direction (FIG. 2C).
The techniques below are a result of surveys on techniques to reduce specimen drift effect. PTL 1 discloses a drift compensation technique of SEM. In Embodiment 1 of PTL 1, a plurality of multi-frame integrated images are taken by the fast-scan mode and then the multi-frame integrated images are integrated while the image shifts between the images are compensated for in order to obtain a target image less affected by the drift through the fast-scan mode.
PTL 2 discloses a technique for making it possible to compensate for various types of image shift caused by drift occurring during imaging. In PTL 2, SEM images are taken within a short period of time before and while a characteristic X-ray image is being obtained, and the plurality of SEM images are divided into a plurality of small domains, respectively. The amounts and directions of shifts between the small domains are calculated and represented by two-dimensional vectors to obtain not only the shift caused by translation of images for compensation during imaging of the characteristic X-ray image, but also components, such as scaling, rotation and trapezoidal distortion, to adjust the driving amount of a specimen stage or the control amount of a deflector coil.
Since scanning distortion caused by electronic circuitry is one of the factors that distort electric charged particle beam images, techniques for reducing the effect of the scanning distortion also have been surveyed.
PTL 3 discloses a method for correcting a TV scan image I2, which is distorted in the scanning direction due to scanning errors made while the TV scan image is scanned at a high scan rate, by using a slow scan image I1, which is taken at a low scan rate and therefore has ignorable scanning errors.